What was originally supposed to be a seven-week mission has pressed on for much longer, a fantastic feat for the space industry. Tomorrow marks the 10th anniversary of Opportunity’s landing on the Red Planet, and today, its findings—along with Curiosity’s—have been published in the journal Science.

Martian sand dunes closely resemble those on Earth in shape and texture.

Opportunity has filled most of its days cruising the sulphate-rich plains of a region called Meridiani Planum. But in August 2011, it reached Endeavour crater, a 22-kilometre-wide hole carved out by a meteorite impact about 4 billion years ago. As Opportunity moved south, scientists studying a spectrometer aboard the Mars Reconnaissance Orbiter noticed a pile a clay-rick rocks to the west of Matijevic Hill, where Opportunity was at work.

Here’s Alexandra Witze, writing for Nature:

The Matijevic rocks lay beneath those kicked up by the meteorite impact that created Endeavour crater, suggesting that they must already have been there when the impact occurred. “We’re looking at the oldest rocks we’ve ever seen with Opportunity,” says Arvidson.

In other words, the oldest environment known on Mars was a watery, pH-neutral one that could have been habitable for life as we know it. Later, after the impact, the water became more acid- and sulphate-laden, and less suitable for life.

This has helped scientists see further and further back in time, to a period when Mars’ landscape was richer and more varied than we’d suspected. In December, Curiosity’s Chemistry and Camera (ChemCam) instrument picked up a hydrogen signal in a representative soil sample, suggestive of a highly evolved planet with rivers and groundwater. With evidence of similar environmental conditions at both Curiosity’s and Opportunity’s landing sites—despite their separation in time and space—experts are developing a better picture of how the planet may have come to be habitable, and how it had opportunity for growth early on.

Meanwhile, Opportunity is still chugging along, finding new oddities to assess. On January 8 of this year, it upturned a piece of rock with an unusual chemical composition. Scientists hope to look more closely at rocks like these in the hopes that they can provide evidence for how many different types of habitable environments Mars might have had.

Examine the anatomy of a Mars rover with our interactive, based on twin rovers Opportunity and Spirit.